Some embodiments of the invention relate to an aircraft seat attachment provided with a system for maintaining a clamping force by friction. Some embodiments of the invention relate to an aircraft seat attachment provided with a system for locking an activation lever.
Aircraft passenger seats are generally mounted on a rail 1, as shown in FIGS. 1a and 1b. The rail 1 is a section having an upper lip 2 onto which the seat attachment is clamped, this lip 2 being machined to enable the insertion of the lower part of the attachment (bosses) under the lip of the rail.
A seat is generally fixed to the rail by means of at least three attachments, typically four, two at the front of the seat and two at the rear. A passenger seat attachment 3, such as that shown in FIG. 2, must typically fulfill two principal functions, namely:                clamping the attachment 3 to the lip 2 of the rail to prevent any movement, and        for the rear attachments, transferring longitudinal loads, for example in the event of a crash, from the seat to the rail.        
To this end, the attachment 3 comprises at least one boss 6 to be positioned under the lip 2 of the rail. This boss 6 is either fixed relative to the attachment 3, in which case the attachment 3 includes a plunger 8 configured to vertically translate relative to a body 4 of the attachment (cf. FIG. 2), or the boss 6 is configured to vertically translate relative to the body 4 of the attachment 3.
To fix the seat to the rail 1, the boss 6 enters the hole in the rail and then moves longitudinally along the length of the rail by a half-pitch of the hole to be located under the lip 2 of the rail 1. The boss 6 is then moved vertically in order to come into contact with the lower face of the lip 2 and create a positive clamping action on the lip 2 of the rail.
Two techniques are usually employed to generate the force clamping the attachment to the lip 2 of the rail:                using a screw to move the boss 6 or the plunger 8 vertically; in this case, a hand tool is necessary and the clamping torque must be controlled in order to guarantee the clamping effect; this solution also enables infinite adjustment, making it possible to compensate for the tolerances of the parts used, or        using a system with no adjustments, possibly requiring the use of a hand tool, generally using a spring effect of a spring member 9 (spring washer, elastomer block, spring, etc.), enabling geometrical tolerances to be compensated and guaranteeing the required clamping.        
If necessary, longitudinal loads are transferred to the rail by a shear member 10 on a lower face of the plunger 8 accommodated in the holes in the rail.
Systems with no adjustment generally employ an activation lever 11. In most cases the lever 11 generates the clamping effect and the line B1 of the clamping force passes through the lever 11, as can be seen in FIG. 2. A locking system 12 is used to hold the lever 11 in place, situated for example at one end of the lever 11. This system 12 is formed by a hook 121, for example, adapted to cooperate with a stud 122 that is part of the body 20 when the lever 11 is in the locked position. However, some of these locking systems do not sufficiently secure the seat to the rail 1. In fact, the lever and/or the locking system often remains in an unstable locking position (cf. FIG. 3), wherein the lever and/or the locking system does not enable the energy peak corresponding to the clamping effect to be maintained in the event of stresses exerted on the attachment, such as vibration. In other systems, this locking position is not clearly identifiable.